We're currently flying mostly blind as far HTTPS metrics go; we don't know, for example, what percentage of users supports which versions of TLS or ciphers, or (soon) SPDY/HTTP2. We do have some NavTiming metrics but we don't have a great way of displaying these (dashboards).
We should get more insight there. I've previously experimented with nginx lua + statsd plugin that logged ciphers & protocols and it did work fine but we should think of it more eloquently and deploy it. Probably blocked on T86648.